Electronic digital imaging systems are known in the art in which images are digitized and stored as digital pixel elements in a computer based system. The images can then be retrieved and displayed on display mechanisms for later use. An example of this type system is the medical field where x-ray images, computed tomography (CT) scan images, magnetic resonance imaging (MRI) data, ultrasound data and the like may be digitized and the images can be stored and retrieved from a mass storage device. By connecting a graphics monitor or a plurality of monitors to the system, a medical practitioner can retrieve the images on such a monitor on demand.
Various types of quality control have been applied to electronic digital imaging systems. For example, in U.S. Pat. No. 4,939,581 to Shalit, an attempt is made to measure the quality of gray-scale of a video monitor screen by placing a gray-scale test pattern on the CRT screen and measuring features of the test pattern using a photometer. The gray-scale test pattern is then photographed using an electronic camera, a hard copy film is produced from the electronic camera image and a densitometer reading is taken of the hard copy. The results of the densitometer readings are then used to adjust the electronic camera image for ideal luminance to compensate on a pixel-by-pixel basis to produce a gray-scale which matches the developed film.
The system of the Shalit patent only addresses control of a single image quality aspect: the gray-scale accuracy of hard copies as representations of the CRT image. In addition, the system does not treat the case of matching a CRT display to film and does not address the problem of the original CRT image quality. Since the Shalit system is only designed to match a hard copy to a CRT device, an objective display of image quality is ruled out. In order to reproduce accurate images, an objective standard needs to be applied to CRT matching and to locate sources of degradation throughout all points within an electronic imaging system, not just through the CRT display device. Without any form of system- wide degradation analysis, components of the Shalit system may affect the overall image quality of the video monitor causing the x-ray to match the video monitor for a wholly inaccurate display.
In U.S. Pat. No. 5,115,229 to Shalit, a method and system in video image reproduction is described using a gray-scale test pattern on CRT screens to compare two or more video screens. The objective of this system is to achieve a CRT-to-CRT match without regard to an objective set of criteria for CRT alignment. One of the drawbacks of the Shalit system is that k will match a good CRT with a bad CRT display such that both CRT displays will produce imagery only up to the capabilities of the poorest of the two screens. There is no ability to match the CRTs to any objective criteria to not only align the CRTs to produce the best image quality possible from that particular CRT but also to locate CRTs operating below a minimum acceptable threshold. In addition, the Shalit system merely deals with a single image quality aspect: the gray-scale accuracy between CRTs. There is a need in the art therefore to control the image quality in many categories simultaneously such as pixel value, geometric and spacial resolution characteristics.
In the paper entitled "Quality Monitoring of Soft-Copy Displays for Medical Radiography" by Reiker et al., published in the Journal of Digital Imaging, August 1992, luminance measurements from a plurality of CRT screens within a hospital or imaging center are used to compile a database of luminance information. A low cost photometer instrument with an RS-232 interface allows the device to be connected to CRT screens throughout a hospital to measure the luminance values on every display station. A software method and procedure for displaying test images of single valued luminance information allows a software program to generate luminance response curves for every display device within the organization. This provides a system for quality control of the CRT displays. The author has described this system as being necessary to calibrate the CRTs to conform with a standard luminance curve by adjusting brightness and contrast controls of the CRT stations. The shortcomings of this system, however, are that the lack of image quality control throughout the entire electronic imaging system may result in erroneous adjustments being made to CRTs at the various locations throughout the network.
There is a need in the art to control the quality of the image within an electronic digital imaging environment which is unsatisfied by existing systems. Present electronic digital imaging systems lack the ability to test, maintain and ensure the integrity of the quality of the image throughout all stages of the system including the stages of acquisition, transmission, display and hard copy generation. There is also a need in the art to measure and report system performance to a system operator in a user-friendly manner such as a simple go/no-go indicator of acceptable system performance. Further, there is a need in the art for remote diagnostic testing, predictive and preventative servicing and computer assisted fault isolation of image degradation and system failures. There is also a need in the art to provide system performance testing by using the components of the system to test themselves without the need for a field service person to carry expensive test and calibration equipment to the site. The present invention solves these and other problems which will be recognized by those skilled in the art upon reading and understanding the following specification.